X-ray polarization changes with the state transition in Cygnus X–1

Jana, Arghajit; Chang, Hsiang-Kuang

doi:10.1093/mnras/stad3961

Cited by 8 publications

(1 citation statement)

References 49 publications

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“…A preliminary look at the polarimetric results was posted in an Astronomer's Telegram (AT; Dovciak et al 2023), motivating a rich multiwavelength campaign to supplement IXPE's later epochs, including complementary X-ray spectral coverage during epochs 3-5 with NuSTAR, NICER, INTEGRAL, AstroSat, and Swift, as summarized in Table 1. IXPE polarimetric results from epochs 1-3 were published by Jana & Chang (2024); their presentation of the polarimetric measurements is aligned with those of the AT and what we present here, although our conclusions differ from the ones of Jana & Chang (2024).…”

Section: Datasupporting

confidence: 81%

An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

Steiner,

Nathan,

et al. 2024

ApJL

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We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.

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Section: Datasupporting

confidence: 81%

An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

Steiner,

Nathan,

et al. 2024

ApJL

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X-ray view of dissipative warm corona in active galactic nuclei

Palit,

Różańska,

Petrucci

et al. 2024

A&A

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Detections of the X-ray spectra of active galactic nuclei (AGNs) typically reveal a noticeable excess of soft X-rays beyond the extrapolation of the power-law trend observed between 2 and 10 keV. However, the cause of this surplus remains unclear. In the scenario of soft Comptonization, observations suggest a warm corona temperature, ranging from 0.1 to 1 keV, and an optical depth of approximately 10 to 30. Furthermore, according to radiative constraints derived from spectral analyses employing Comptonization models, it has been suggested that most of the accretion power is released within the warm corona. At the same time, the disk beneath it is largely non-dissipative, mainly emitting the reprocessed radiation from the corona. We tested the dissipative warm corona model using the radiative transfer code TITAN-NOAR on a sample of 82 XMM-Newton EPIC-pn observations of 21 AGNs. Based on a spectral modeling of the X-ray data, we aim to estimate the total amount of internal heating inside the warm corona on top of the accretion disk. By modeling the 0.3--10 keV EPIC-pn spectra with the TITAN-NOAR model component, we estimated the internal heating and optical depth of the warm corona and checked their correlations with such global parameters as the hot corona spectral index, black hole mass, and accretion rate. From the model normalization, we computed the radial extent of the warm corona on top of the cold accretion disk. Our model infers the presence of dissipative warm corona, with optical depths distributed across the range of sim 6--30 and a total internal heating in the range of sim 1--29 times 10$^ $\,cm3. We do not detect any variation between these properties and global properties, such as the black hole mass and accretion rate. The extent of the warm corona is spread across a broad range, from 7--408 gravitational radii, and we find that the warm corona is more extended for higher accretion rates. Soft excess emission is ubiquitous across a wide mass range and accretion rate in AGNs. We confirm that the warm corona responsible for producing the soft X-ray excess is highly dissipative with greater optical depths being associated with lower internal heating and vice versa. The cold standard accretion disk regulates the extent of the warm corona.

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Polarized X-rays correlated with the short-timescale variability of Cygnus X-1

Ninoyu,

Uchida,

Yamada

et al. 2024

Publications of the Astronomical Society of Japan

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We systematically investigate the variability of polarized X-rays on a timescale of a few seconds in the low/hard state of the black hole binary Cygnus X-1. The correlation between polarization degrees and angles with X-ray intensity was analyzed using data collected by the Imaging X-ray Polarimetry Explorer (IXPE) in 2022 June. Given that X-ray variability in the low/hard state of Cygnus X-1 is non-periodic, flux peaks were aggregated to suppress statistical fluctuations. We divided the temporal profiles of these aggregated flux peaks into seven time segments and evaluated the polarization for each segment. The results reveal that the polarization degree was 4.6% $\pm$ 1.2% and 5.3% $\pm$ 1.2% before and after the peak, respectively, but decreased to 3.4% $\pm$ 1.1% and 2.7% $\pm$ 1.1% in the segments including and immediately following the peak. Furthermore, the polarization angle exhibited a slight shift from approximately 30$^{\circ }$ to ${\sim} 40^{\circ }$ before and after the peak. These findings suggest that the accretion disk contracts with increasing X-ray luminosity, and the closer proximity of the X-ray emitting gas to the black hole may lead to reduced polarization.

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X-ray polarization changes with the state transition in Cygnus X–1

Cited by 8 publications

References 49 publications

An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

X-ray view of dissipative warm corona in active galactic nuclei

Polarized X-rays correlated with the short-timescale variability of Cygnus X-1

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